This invention relates to a method of manufacturing mechanically strong foamed plastics or rubber moldings and to the products thereof.
In recent years, foamed articles of plastics or rubber have come to be used in increasing quantities in wide fields in view of various features thereof such as excellent heat insulating, shock and sound absorbing and cushioning properties, and a high buoyancy. Foamed articles used to date have been improved primarily in the heat insulating and cushioning properties and so on. Accordingly, foamed articles consisting of fine cells have been accepted all the more favorably. These cells had an average diameter of less than 0.5 mm and a wall thickness of several microns.
Quite recently, however, many attempts are made to apply foamed articles as structural material and consequently there arises growing demand for foamed product having great mechanical strength. To meet this demand, there is proposed the process of forming a layer of skin on foamed articles or enlarging individual cells with their walls more thickened. Though somewhat improved from the standpoint of providing structural material, the conventional process of incorporating a foaming agent in synthetic polymers and thermally expanding the mass can not fully attain the object, offering only limited applications.